The present invention relates to a method of etching oxides on a substrate to minimize or prevent deposition of contamination on the substrate. In particular, the present invention relates to the etching of silicon oxides.
In integrated circuit manufacturing, the etching of oxides is typically carried out using a halide-containing water solution, for instance a HF/water solution, or reactive ion etching (RIE). The former method is not compatible with integrated processing of integrated circuits while the latter damages the surface of the substrate and contaminates the near-surface region of the substrate. As a result, neither method permits integration of oxide etching with other steps performed in a cluster processor.
The use of gaseous HF and water vapor, for example, is an alternative to RIE for gas-phase oxide etching. In this process, water vapor is needed to uniformly initiate etching. Gas phase etching can produce the same level of hydrogen termination as the traditional HF/water rinse process. The process is well developed and is supported by commercial reactors. It works on the premise that the HF-water vapor mixture delivered to the oxide condenses there, and hence, the etching process is eventually taking place in the liquid phase. One of the problems encountered with this etching mode is that some of the reaction products may precipitate on the surface where they are difficult to remove without an additional deionize water rinse. Also, difficulties with precise control of the condensed liquid film composition and its uniform coverage of the oxide may, under certain conditions, result in inadequate etch uniformity and run-to-run reproducibility. Moreover, since existing HF vapor etch chemistry generally involves the addition of water vapor, the process is difficult to integrate with reduced pressure reactors and stainless steel components.
U.S. Pat. No. 5,022,961 to Izumi et al., incorporated herein by reference, implements an approach in which etching is performed using HF and alcohol where water added to the system is minimized. Etching is performed at room temperature and atmospheric pressure and liquid as well as vapor state etching are contemplated. Ionic contaminant, however, remains on the surface after etching, contained within the alcohol layer. After-treatment is again required to remove the contamination.
Prior art etching techniques suggest that use of particular solvent molecules for etching in certain circumstances. Izumi et al., for instance, discusses etching with HF or other halide-containing species only in combination with alcohol. Wet etching has prevalently been disclosed with HF, water and acetic acid alone or a mixture of organic acids. U.S. Pat. No. 4,746,397 to Maeda et al. does disclose etching with the use of a fluorine-containing species and an alcohol ketone or carboxylic acid. However, liquid or vapor phase etching is contemplated under reduced pressure where the addition of water is specified.
It is disclosed in U.S. Pat. No. 4,857,142 to Syverson and U.S. Pat. No. 4,749,440 to Blackwood that etching may be accomplished with a minimum of added water where the oxide itself contains sufficient water. It is thus considered in the art that at least some water is required for etching.
Drawbacks of prior practice are addressed by the present invention in a method of etching oxides on a surface of a substrate comprising etching at a preset wafer temperature with a gas phase mixture of a halide-containing species and a low molecular weight organic molecule having a high vapor pressure at standard conditions, in an enclosed chamber at a pressure such that all species present are substantially maintained in the gas phase and condensation of species present on the etched surface is controlled. Because trace water vapor may appear in the process chamber, water vapor is taken into account as a species present in the gas phase. Because water is less volatile than the constituent reactants, the temperature and pressure parameters are chosen from the area below the curve for water in the phase diagram. By maintaining temperature and pressure parameters within this range, all species present in the chamber, including water, are substantially maintained in the gas phase. Low molecular weight organic molecules having high vapor pressure at standard conditions encompass low molecular weight alcohols, organic acids, ketones or alkanes such as methanol, isopropanol, acetone, acetic acid and methane. Preferably, etching is performed in a cluster dry tool apparatus. The process achieves controlled, gas-phase etching of oxides with etch rates up to two orders of magnitude lower than typical rates obtained for vapor HF/water etching, without the addition of water vapor to the input gases.
The present invention also addresses drawbacks of prior practice by a method of etching oxides comprising etching with a halide-containing species and water where the pressure and temperature parameters are, as discussed above, selectively chosen from parameters below the curve representing water in the phase diagram.
It is an objective of the present invention to provide a method of etching oxides in which the oxide etch rate is controlled.
It is an objective of the present invention to provide a method of etching oxides in which condensation of species present on the etched surfaces is controlled.
It is a further objective of the present invention to provide a method which controls etch at a rate of up to two orders of magnitude lower than typical rates obtained for vapor HF/water etching.